As the offense left the field, Ron Rivera gathered the Chargers defense around him earlier this month and for several minutes let them know he was not pleased with the execution in a certain period of that day's practice.

Nor was the defensive coordinator pleased with how he and his staff prepared for or reacted to that period.

“We weren't clear on what had to be done,” Rivera said later. “I told them it's as much a reflection on me and the coaches as it is on them — so they understand we're all in this together.”

The new sheriff is rounding up his defense with a message of accountability and preparedness.

Yes, the plan is for last year's disappointing defense to be turned around with the return of Shawne Merriman and the arrival of Larry English and Kevin Burnett.

But moreover, clarification, simplification and attention to detail are marking the beginning of the Rivera era.

Sure, Rivera has implemented a more aggressive approach, has tweaked alignments and play-calling philosophy. But what he did to the playbook, and how he and his staff are coaching on the field and in meeting rooms is as important (perhaps more) than any of those things.

“It doesn't matter what I call, as along as we execute it properly, we've got a chance,” Rivera said. “If we can make sure the guys understand things and we're detailed in what we do while we're practicing, we should have success.”

Football happens fast. Things don't always go according to plan. It can get confusing if you don't know what you're doing, and know it like the alphabet.

“Football is 80 percent mental, 20 percent physical,” linebacker Stephen Cooper said. “ . . . A lot of things we were doing last year, there was a lot of uncertainty on the whole group. This year we're applying what we're learning in the classroom on the field.”

Most Chargers starters are expected to play the first half of tonight's exhibition game at Arizona. In that time, the defense will measure itself against a Cardinals offense that, even in the preseason, gives a lot of looks. It will be a decent test for a defense that has so far looked sharp in practice and (in a dumbed-down version of itself) the preseason opener last week.

Gone is the finger-pointing and shrugging that characterized the 2008 defense, a unit that allowed the sixth-most touches, ninth-most yards and second-most passing yards and got itself a new coordinator midseason when Ted Cottrell was fired after the team's dreadful trip to Buffalo and London.

“There is a lot of gray area taken out,” safety Clinton Hart said. “That has been the problem in the past with certain calls and ways you play things. It really cleaned things up and simplified it for us.”

After a year-and-a-half as linebackers coach and half-season as coordinator, Rivera was able to evaluate each player's strengths and weaknesses and what they were able to do collectively.

When the defensive staff went through the playbook this offseason, it threw out some things and added some others. And even the existing parts got a remodel. Each play has a sort of appendix, where every conceivable variable is covered. That's the way it is taught on the field, as well, so that players don't have excuses.

This is by no means D light, but it is, by the way it's taught, simpler.

“They're putting a lot more stuff in; they're putting a lot on us,” safety Eric Weddle said. “But they're giving us every explanation. Every question that we have, it's already given. . . . Whether it was coaching, whether it was us, we just weren't on the same page (last year). Now, if there's a mistake or the coverage isn't right, it's on us.”

To try to avoid that, the repetition is relentless.

“It's different for us, so sometimes you get annoyed at it,” cornerback Quentin Jammer said. “ . . . Over and over and over and over and over. But you hear it and hear it, and all of a sudden you just get it and it carries over to the practice field.

“I think it's exactly what we need. There are a lot of different personalities on this defense. This is what we need to be to get us where we need to be, to be an elite defense.”